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Inspect and Analyse

Around 80% of all machine breakdowns are due to contaminated oil and poor filtering – but most of them could be avoided with regular checks in the form of analyses and other inspections of the oil and filters.

Visual inspection

In small systems it is not really financially viable to conduct regular lab analyses on the hydraulic oil, but doing a basic visual inspection every week (or a similar interval) will protect the system against disruptions, damage, and sudden unexpected stoppages.

Here is a useful chart for visual inspections:

The oil’s appearancePossible causeAction/recommendation
Light and clearNormalThe oil can be used
Turbid, unclearThe oil is contaminated with emulsified waterAnalyse/change the oil
Free (entrained) waterThe system is contaminated with waterDrain the water
Dark, smells burntThe oil has oxidisedAnalyse/change the oil
Visible contaminantsContaminants, wear particlesAnalyse/change the oil/check filters

Oil analysis
In large hydraulic plants, which often contain hundreds of litres of hydraulic oil, it is common to regularly check the status of the oil and the system via oil analyses.

An oil analysis can answer questions such as:

  • What is the condition of the oil?
  • Is there any severe wear?
  • What type of wear?
  • Where in the machine is the wear happening?
  • Is the pipe system clean?
  • Is filtration working as it should?
  • Does the contaminant level in the oil risk causing problems in the future? E.g. wear, corrosion, jammed valves etc.

Regularly analysing the chemical and physical state of the oil makes it possible to identify machine problems before they grow too big, reduce down times, plan maintenance intervals, reduce maintenance costs and optimise oil drain intervals.

Troubleshooting in a hydraulic system

TroubleshootingPossible cause
No movement on start-up 
  • Oil level too low
  • Wrong oil quality
  • Oil viscosity too high
  • Air in the system
  • Blocked suction filter
  • Leaky pressure relief valve
  • Mechanical fracture in the system
  • Worn pump
Too slow movement 
  • Worn pump
  • Air in the system
  • Leak in suction pipe
  • Leaky suction pipe
  • Leaky pressure relief valve
  • Worn pump gasket
Uneven movement 
  • Air in the system
  • Damaged accumulator
  • Piston seal too narrow
Movement stops during operation 
  • Oil level too low
  • Hydraulic hose rupture
Operating pressure too low 
  • Leaky oil pipes/hoses
  • Leaky valve
  • Contaminants in valve
  • Worn valve
  • Defective valve seats
Abnormal noise in the system 
  • Air in the system
  • Contaminants in oil filter
  • Oil level too low or oil viscosity too high
  • Too little oil in the pump’s suction pipe
  • Spring in pressure relief valve or check valve is too weak or defective
Oil gets too hot 
  • Wrong oil viscosity
  • Contaminants in the oil
  • Level too low
  • Contaminants in the pressure relief valve
  • Worn pump
Foaming oil 
  • Air in the system
  • Oil level too low
  • Wrong oil quality
  • Contaminated oil
  • Reservoir baffle wrongly positioned


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